Seoul, Jan 31 : A one-on-one debate between South Korean ruling party's presidential candidate Lee Jae-myung and main opposition candidate Yoon Suk-yeol was scrapped on Monday as the two sides failed to narrow their differences over the rules. The conservative People Power Party (PPP) said it failed to reach an agreement with the ruling Democratic Party (DP) even after rounds of negotiations over details of their first two-way debate, scheduled for Monday night, before having an expanded debate with two minor contenders on Thursday, reports Yonhap News Agency. "It seems impossible to hold the debate now," said Rep. Sung Il-jong, the PPP's chief negotiator, saying his DP counterpart did not respond to his call to talk earlier in the day. Whether candidates are required to participate in the debate without reference materials has emerged as a thorny issue during negotiations, although the two sides agreed to hold a free debate with no restrictions on topics. While the DP suggested neither candidate use materials during the debate, the PPP insisted on using reference materials related to Lee's alleged connection to a massive development corruption scandal. Meanwhile, minor candidates Ahn Cheol-soo of the People's Party and Sim Sang-jeung of the Justice Party launched separate sit-ins at the National Assembly to protest the planned one-on-one debate. The two had sought injunctions to stop the three major TV stations from hosting a Lee-Yoon debate, and the injunctions were granted by two courts last week. Following the courts' decisions, the PPP proposed a two-way debate without the involvement of the broadcasters. The DP consented while also demanding Yoon's participation in a four-way debate. The presidential election is scheduled to be held on March 9. /IANS